------- Comment #3 from casmyu at gmail dot com 2009-03-10 01:23 -------
Hi:
I have changed the code as you said, but it is more error now.
1 #include <stdio.h>
2
3 int main()
4 {
5 char src[30] = {"This is a test message.\n"};
6 char dst[30];
7 int len = 25;
8
9 __asm__ __volatile__(
10 "cld\n\t"
11 "rep movsb"
12 :
13 // : "(src), "D"(dst), "c"(len)
14 : "+c"(len), "+D"(dst), "+S"(src)
15 );
16 printf("%s\t%d\n", dst, len);
17 return 0;
18 }
[root][~]# gcc -O2 -o bugtest bugtest.c
bugtest.c: In function ¡®main¡¯:
bugtest.c:15: error: input operand constraint contains ¡®+¡¯
bugtest.c:15: error: input operand constraint contains ¡®+¡¯
bugtest.c:15: error: input operand constraint contains ¡®+¡¯
bugtest.c:9: error: input operand constraint contains ¡®+¡¯
bugtest.c:9: error: input operand constraint contains ¡®+¡¯
bugtest.c:9: error: input operand constraint contains ¡®+¡¯
Please help to re-check this issue.
Thank you!
(In reply to comment #2)
> Subject: Re: Excessive optimization issue
>
>
>
> Sent from my iPhone
>
> On Mar 9, 2009, at 8:36 AM, "rguenth at gcc dot gnu dot org"
> <gcc-bugzi...@gcc.gnu.org
> > wrote:
>
> >
> >
> > ------- Comment #1 from rguenth at gcc dot gnu dot org 2009-03-09
> > 15:36 -------
> > You need to specify that the registers are clobbered by the asm.
> > The only
> > way to do that is to use output constraints ("+D", "+c", etc.) on
> > proper
> > temporaries.
> >
> > int lent = len;
> > char *dstt = dst;
> > char *srct = src;
> > __asm__ __volatile__(
> > "cld\n\t"
> > "rep movsb"
> > : "+c" (lent), "+D"(dstt), "+S"(src)
> > );
> > Otherwise GCC thinks the registers still hold the original value.
>
> Oh and mark this inline-ask as clobbering memory.
>
> >
> >
> >
> > --
> >
> > rguenth at gcc dot gnu dot org changed:
> >
> > What |Removed |Added
> > ---
> > ---
> > ----------------------------------------------------------------------
> > Status|UNCONFIRMED |RESOLVED
> > Resolution| |INVALID
> >
> >
> > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39403
> >
>
--
casmyu at gmail dot com changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |casmyu at gmail dot com
Status|RESOLVED |UNCONFIRMED
Resolution|INVALID |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39403
